Referring to FIG. 1, an engine valve 1 for an automobile might comprise a stem 2, and a valve head 4 integrally formed at one end of the stem 2. In particular, when the engine valve 1 is used as an exhaust valve, the valve head 4, because it will be exposed to combustion gas from the combustion chamber and exhaust passages, preferably has high heat resistance. In contrast, the heat resistance of the stem 2 generally need not be as high as that of the valve head 4.
This being the case, there are valves in which a valve head member made, of a metal having high heat resistance is integrally joined by means of friction welding or the like to a stem member made of a metal having lower heat resistance but excellent mechanical strength, for example. A valve made by such a process may be advantageous because it may permit achievement of both durability and cost reduction as a result of judicious selection of metals having properties respectively suitable for the valve head and the valve stem.
Although the description which follows is given in terms of the example of a valve in which a friction-weld joint or other such stem joint is employed to join a head member and a stem member of an engine valve, the present invention is not limited to engine valves but may be applied to friction-weld parts in general. Furthermore, the present invention is not limited to friction-weld joints or stem joints but may be applied to detection of flaws in general; for example, the present invention may be used to detect flaws at joints between metal parts regardless of the type of joint employed to join those parts.
One type of device that may be used for inspection of a welded joint is an apparatus including a sensor unit equipped with an eddy-current flaw detection sensor and an ultrasonic flaw detection sensor. The sensor unit might move along a welded joint, and, when the eddy-current flaw detection sensor detects a surface flaw on the joint, the sensor unit might stop moving at the position where the surface flaw is detected to inspect the interior of the joint (hereinafter referred to as “internal flaw inspection”) through use of an ultrasonic flaw detection sensor.
While such an inspection apparatus can be effective for flaw inspection of a joint of a planar metal member, it is less efficiently used to perform an inspection, especially an internal flaw inspection, of an object such as an engine valve which is comparatively small, and whose stem, which may include a joint comprising a friction-weld joint or other such stem joint, has an elongated columnar shape.
In another method for internal flaw inspection of a joint, an ultrasonic flaw detection sensor is made to face an end face of a rod-like metal member having the joint in the longitudinal middle thereof in such fashion as to cause an ultrasonic wave to enter from the end face of the rod-like member. It should be noted that this method is preferably carried out with interposition of a contact medium (for example, water or oil) between the ultrasonic flaw detection sensor and the end face of the rod-like member to increase transmission efficiency of the ultrasonic wave. This method therefore tends to be troublesome, and automation of internal flaw inspection is difficult when this method is used.
Further, in another method for internal flaw inspection of a joint of a rod-like metal member, an ultrasonic flaw detection sensor might be provided in a tank filled with water as contact medium and a rod-like metal member might be held in such fashion as to cause the end face thereof to face the ultrasonic flaw detection sensor in the water (hereinafter referred to as “water immersion flaw detection method”). In such a situation, if water serving as contact medium is always interposed between the ultrasonic flaw detection sensor and the end face of the rod-like member, this may facilitate automation of internal flaw inspection.
As described above, surface flaw inspection of a stem joint may be performed through use of a surface flaw inspection apparatus equipped with an eddy-current flaw detection sensor, and internal flaw inspection of the stem joint may be performed through use of an internal flaw inspection apparatus equipped with an ultrasonic flaw detection sensor, particularly an internal flaw inspection apparatus configured to hold a valve in such a way that a tip of the stem of the valve faces the ultrasonic flaw detection sensor which is disposed in a tank filled with water serving as contact medium.
However, problems such as the following may arise in connection with flaw inspection of a stem joint of a valve when carried out as described above.
First, two independent inspection apparatuses, that is, a surface flaw inspection apparatus and an internal flaw inspection apparatus, are required, resulting in large equipment size and increasing cost accordingly.
Secondly, cycle time for the flaw inspection process to complete is long even when the two flaw inspection apparatuses are positioned adjacent each other because a valve which finishes inspection by one apparatus must be conveyed to the other apparatus and then loaded into the other apparatus.
There is therefore need for a method and apparatus for flaw inspection of a stem joint of an engine valve that would use an ultrasonic flaw detection probe and an eddy-current flaw detection probe in a manner that would permit downsizing of equipment and shortening of inspection cycle time.
In accordance with one aspect of the present invention, the two inspection apparatuses are integrated into a single unit. In some embodiments, such integration of the two inspection apparatuses makes it possible to downsize the flaw inspection equipment and to shorten the cycle time required for the flaw inspection through one or more of the following: causing an ultrasonic flaw inspection chamber and an eddy-current flaw inspection chamber to be disposed adjacent to each other in a housing; arranging three valve supports at intervals corresponding to a distance between the two inspection chambers one by one in the horizontal direction in which both inspection chambers are adjacent each other; and moving the three valve supports integrally in the horizontal direction and in the vertical direction, so that a new valve at a location outside the inspection apparatus, a valve which has completed inspection in the first inspection chamber, and a valve which has completed inspection in the second inspection chamber can be transferred, respectively, to the first inspection chamber, the second inspection chamber, and to a location outside the apparatus.
The present inventors have constructed prototypes of flaw inspection apparatuses embodying the foregoing features and have verified the advantageous effects thereof.